Acyl-de-hydrogenation

Acylation with Nitriles. The Hoesch Reaction Acylation or Acyl-de-hydrogenation... 

Halogenation of Carboxylic Acids and Acyl Halides Halogenation or Halo-de-hydrogenation... 

Alkylation. Acylation, and Carbalkoxylation of Nitrogen Heterocycles342 Alkylation or Alkyl-de-hydrogenation, etc. 

Discrimination of double-bond geometry by the reaction has also been one of the xmsolved problems in organic synthesis. Geometry-selective acylation and de-acylation of tri- and tetra-substituted olefins have been well developed by enzymatic methods [27 28 and references cited therein]. On the other hand, the non-enzymatic counterpart has scarcely been reported before our report in 2012 [29]. We found that double-bond geometry of tri- and tetrasubstituted alkenediols was effectively differentiated on their acylation via hydrogen-bond-mediated molecular recognition of the substrate structure by the catalyst. DMAP-catalyzed acylation of trisubstituted alkenediol 28 with NHNs substituent gave almost a 1 1 mixture of Z-0Ac and E-0Ac in 55% combined yield, which indicates the similar... 

The key compounds in the synthesis of 4,4 -dithiocello- and -xylotrioses are the per-acetylated 1,4-dithiodisaccharides (43 a, 43 b) (Scheme 14) which are obtained from acylated (39 a, 39 b) by hydrogen bromide treatment and displacement of the halide by potassium or tetrabutylammonium thioacetate. Total deacetylation of the donors and reaction with triflated acceptors (34 a) or (34b) afforded the expected trisaccharides which can be converted after conventional treatment, into free trisaccharides (44d,44e,44g and 44 h) [40]. Using the same stepwise procedure, but with activation of the donor by selective in situ S-de-acetylation and activation, the cellotetraoside (44 i) and cellopentaoside (44j) were obtained in good yield [41]. 

Acylation at a Carbon Bearing an Active Hydrogen Bis(ethoxycarbonyl)methyl-de-halogenation, etc. 

Roger and Mathvink reported on the extensive synthesis of ketones based on the acyl transfer reaction of acyl selenides to alkenes using tin hydride as the radical mediator (Scheme 4-24) [46]. A radical arising from the addition of an acyl radical to alkenes abstracts hydrogen from the tin hydride with the liberation of a tin radical, thus creating a chain. The addition process is in competition with de-carbonylation. In this regard, aroyl, vinylacyl, and primary alkylacyl radicals are most suitable for this reaction and secondary and tertiary acyl radicals are inferior. 

Electroreduction of pyridazines in the presence of acetic anhydride gives the acylated open-chain diamines (cf. 117 -> 222). In aqueous solution a 1,2-dihydropyridazine is formed, which decomposes to nitrogen and an unsaturated hydrazino-aldehyde that polymerizes. Allylic bromi-nation of l,2-dicarbomethoxy-l,2,3,6-tetrahydropyridazine followed by de-hydrobromination gives l,2-dicarbomethoxy-l,2-dihydropyridazine. Catalytic hydrogenation gives the hexahydro compound." ... 

The first step in de novo fatty acid synthesis is the production of malonyl-CoA from acetyl-CoA and bicarbonate. This committed step is catalyzed by acetyl-CoA carboxylase present in the cytoplasm of liver cells and adipocytes. After replacement of the CoA residue in acetyl-CoA by ACP (acyl carrier protein), malonyl-ACP is used to convert acetyl-ACP to butyryl-ACP by the fatty acid synthase complex. In this multistep reaction, NADPH is used as donor of hydrogen atoms and CO2 is produced. Butyryl-ACP is subsequently elongated to hexanoyl-ACP by a similar process in which malonyl-ACP serves as donor of two carbon atoms required for lengthening of the growing acyl chain. This process is repeated until palmitic acid... 

If the nitrile contains also a nitro group, the latter is reduced to an amino group at the same time as the hydrogen sulfide is added. The hydroxyl group of a-hydroxy nitriles should be protected by acylation.79 Hurd and De LaMater80 as well as Walter and Bode81 give comprehensive reports of the preparation and chemical properties of thioamines. 

The use of enzyme technology has also been exemplified in a Chirotech process for the synthesis of both enantiomers of the hydrogenation catalyst DuPHOS (80) [2,86]. A hexanediol mixture consisting of 50% meso and 50% racemic diol 77 was acylated with the aid of immobilized CAL-B (Scheme 23). Only the (i )-configured alcohol was converted by the enzyme and led to the monobutyrate (RyS)-7S and the bisbutyrate RyR)-79. The unchanged (S,S)-diol 77 could be removed by extraction with water and was purified by crystallization from ethyl acetate, to reach an optical purity of 98% ee and 88% de. The mesylate of alcohol (RyS)-7S could be inverted with potassium acetate, and saponification of this acetate and of compound RyR)-79 followed by a crystallization step provided the enantiopure diol (RyR)-77 in 48% yield. Although this procedure was used to produce approximately 30 kg of DuPHOS, it has not been used further for commercial catalyst production. 

A quite different process, called Reppe carbonylation, has been used to convert acetylene to acrylic acid esters. The catalysts are carbonyls of iron, cobalt or nickel and the hydrogen source is a hydrogen halide, HX. The process is thought to involve oxidative addition of HX to the metal carbonyl, followed by coordination and insertion of alkyne into the M—H bond and insertion of CO into the M—C bond. The resulting acyl complex is cleaved by alcohol to produce the ester and the metal hydride catalyst. De Angelis et al. have reported a theoretical analysis of the Ni(CO)4 system. 

Synthesis of enol triflate from N-acylated lactam has been reported. Comins synthesized (5)-pipecolic acid 33 (Scheme 19) from enol triflate 30 of piperidone derivative 29 by Pd-catalyzed carbonylation followed by aymmetric hydrogenation nsing a mthe-nium catalyst with (i )-BINAP. Preparation of the first enantiopure lactam-derived enol triflate from (5)-pyroglutamic acid was achieved, and the synthesis of a proline analog was obtained in good yield (86% de). ... 

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